In a semiconductor device such as an MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor), it is possible to use a built-in diode as a reflux diode. There is proposed a method of building in and utilizing a Schottky barrier diode as a reflux diode (for example, see Patent Document 1).
For example, in the case in which a pn diode is built in a structure of a semiconductor device such as an MOSFET, there is caused a problem in that a recovery loss is increased when the pn diode is operated in the use of a built-in Schottky barrier diode. For this reason, it is desirable that a unipolar current caused to flow by the Schottky barrier diode should be large in a state in which the pn diode is not operated (a bipolar operation). At this time, it is desirable to increase the unipolar current without enlarging a chip area, that is, to increase a unipolar current density, in order to reduce a chip cost. In other words, it is desirable that a component of a reflux current should be constituted by only the unipolar current and the unipolar current density should have a great maximum value at that time. For this reason, there is proposed a method of causing an impurity concentration of a first conductivity type in a region provided directly under a Schottky electrode between adjacent well regions to be higher than that of the first conductivity type of a drift layer in the same region, thereby increasing a unipolar current density (for example, see Patent Document 2).